Sensing structure of alignment of a probe for testing integrated circuits

ABSTRACT

A sensing structure is presented for use in testing integrated circuits on a substrate. The sensing structure includes a probe region corresponding to a conductive region for connecting to the integrated circuit. A first sensing region at least partially surrounds the probe region. A plurality of sensing elements connects in series such that a first of the plurality of sensing elements has two terminals respectively connected to the first sensing region and the probe region. And a second of the plurality of sensing elements has two terminals respectively connected to the probe region and a first reference potential.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/155,623 filed on Jun. 8, 2011, and claims the priority benefit ofItalian patent application number VI2010A000159, filed on Jun. 10, 2010,the disclosures of which are both hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a structure for use in testingelectronic components in a substrate. Moreover, the present inventionrelates to a substrate including one or more sensing structures and atesting equipment for testing electronic components on a substrate.

BACKGROUND

Thanks to advances in the field of manufacturing processes of electronicintegrated circuits, electrical components have become smaller, therebyallowing for manufacturing substrates that include a large number ofintegrated circuits. Moreover, it is possible to fabricate compactelectronic circuits including a large number of components.Consequently, the density of connection terminals for connecting theintegrated electronic circuits with other electronic systems has alsodrastically increased.

After being formed in the substrate, called a wafer, the integratedcircuits need to be tested so as to eventually remove faulty componentsor repair them if this is possible. The functionality of each integratedcircuit included in the substrate is verified by means of suitableprobes that contact the connection terminals or pad of the integratedcircuit to be tested, in technical language called DUT (Device UnderTest). More precisely, during the testing process, an automated testingequipment ATE or tester is electrically connected to the wafer on whichthe electronic components are formed. The interface between the ATE andthe wafer is a card of probes, generally called a probe card, includingseveral probes adapted to simultaneously contact the pads of the DUTintegrated circuits performing the so-called probing action of theprobes on the pads. Said testing procedures of electronic integratedcircuits are commonly performed, for example, during electrical test onthe wafer, called in technical language Electrical Wafer Sort (EWS), orfor a reliability test on wafer, called in the art Wafer Level Burn-in(WLBI).

Since the DUT to be tested includes a very large number of pads close toeach other, the probability that the tip of the probe contacts theregion surrounding the pad increases. Consequently, the probability ofdamaging the passivation surrounding the pad, due to improperlyperformed probing, increases.

In order to avoid damaging the pads and breaking of the passivation, itis therefore crucial to correctly align the tips of the probes of theprobe card with corresponding pads in the testing phase of the DUTintegrated circuits.

The correct alignment of a probe card with respect to corresponding padscan be electrically performed by using suitable dummy (fictitious)structures formed on the substrate. Examples of such dummy structures ordummy pads are shown in FIGS. 34 and 35. In particular, FIG. 34illustrates a pad 10 including a first non-conductive region 12, whichwould be used for the probing in a common conductive pad, surrounded bya conducting region 11 for sensing. A sensing circuit 13 is connectedbetween the conducting sensing region 11 and a ground electrode. Thesensing circuit 13 may be a diode, a resistor or the like. Thedimensions of the non-conducting region 12 substantially correspond tothe dimensions of the connection terminal or pad of the integratedcircuit to be tested. In order to verify alignment, the probe tipcontacts the dummy pads and a current is forced/absorbed by means of thetip. If the tip contacts the first non-conductive region 12, no currentwill flow through the pad, and the circuit will be open. On thecontrary, if the probe tip contacts the conducting sensing region 11, acurrent will flow through the pad and a suitable voltage will bedetected across the sensing circuit 13, thereby indicating that theprobes of the probe card are not correctly aligned with the pads.Several configurations of the dummy pad of FIG. 34 are described in U.S.Pat. No. 7,616,020 (incorporated by reference).

FIG. 35 illustrates a further realization of a dummy pad 20 according tothe prior art. The dummy pad 20 includes a probe region 22 forcontacting the tip of the probe surrounded by a plurality of conductivesensing regions 21 electrically isolated from each other. Eachconductive sensing region 21 is connected to a ground electrode througha sensing circuit 23, 24, 25, 26. Sensing circuits 23, 24, 25, 26connected to different conducting sensing regions 21 may be diodes of adifferent area so as to have a different resistance or may be formed bya different number of identical diodes connected in parallel to thesensing region and a ground electrode or ground terminal. As previouslydescribed, a current is forced from the probe in order to determine theposition of the probe, which, if connected to a conducting sensingregion 21, will be connected to a particular sensing circuit 23, 24, 25,26 in turn connected to a corresponding conducting sensing region 21.Since sensing circuits connected to different conducting sensing regionshave different resistances, it is possible to determine which conductingsensing region is being connected to the probe, thereby indicating thedrift direction of the probe. The sensing circuits may include diodes ofdifferent areas as well as resistors or transistors. Severalconfigurations of the dummy pad depicted in FIG. 35 are described U.S.Pat. No. 7,612,573 (incorporated by reference).

However, the dummy pad 10 illustrated in FIG. 34 only allows detectingwhether the probe contacts the sensing structures within or outside theprobe region but does not allow determining the drift direction of theprobe.

Further, although the dummy pad 20 of FIG. 35 allows determining thedrift direction of a probe, the position of the probe is determined byusing either a different diode for each sensing region or a differentnumber of identical diodes connected in parallel. Accordingly, thevoltage difference measurable between the sensing regions is rathersmall. More precisely, if the sensing circuits are formed by diodes,said voltage difference lies between 50 mV and 100 mV, which is muchless than the threshold voltage of the diode forming the sensingcircuit.

However, in the testing process, it often occurs that the probe tip doesnot contact the corresponding connection terminal perfectly, due, forinstance, to oxidation of the tip itself or to imperfections of the pad.This increases the contact resistance between the probe and theconnection terminal, thereby causing a variation in the value ofmeasured electrical parameter. This behavior is illustrated in thehistograms of FIGS. 36 and 37. In particular, FIG. 36 shows voltagevalues measured in a case where the probe tip perfectly contacts a padwith a characteristic identical to those of a generic sensing region. Onthe other hand, if the measuring conditions are not optimal, asignificant percentage of measurements will provide a voltage valuewhich can vary by 300 mV and even more from the value measured inoptimal/ideal conditions.

Consequently, the structures described in the cited prior art documentsare either not capable of determining the drift direction of the probeor will fail to correctly determine the position of the probe in asignificant number of measurements.

Moreover, since sensing circuits of different sensing regions areconnected in parallel, if the probe tip contacts two neighboring sensingregions, the current will flow through both sensing circuits and thevoltage drop that will be measured across both sensing circuits willmake it impossible to even approximately determine which sensing regionthe probe is contacting.

Finally, sensing circuits including integrated resistors may not beaccurate since the value of a resistor generally varies, in absoluteterms, even more than 25% from the desired value, due for instance tothe unevenness of the process parameters in a manner which is known tothe skilled persons. In addition, integrated resistors may be quitebulky thereby causing the sensing circuits to occupy a large area in thesubstrate and increasing costs.

Given these problems with the existing technology, it would beadvantageous to provide a sensing structure that has reduced dimensionsand is capable of determining the position of a probe in a reliablemanner without being affected by poor electrical contact between theprobe and the sensing structure.

SUMMARY

Embodiments provide a sensing structure, wherein the difference betweenvoltage values of different sensing regions is larger than the variationin the measured value due to imperfections of the testing system. Thisenables unambiguous determination of the position of a probe withrespect to the sensing structure even in the case that the measurementis not performed in optimal conditions.

In accordance with an embodiment, a sensing structure for use in testingintegrated electronic components on a substrate is provided. The sensingstructure comprises at least two sensing regions connectable to a probeand at least one first sensing element. Each of the at least one sensingelement is connected, for example directly connected, to two sensingregions such that for each sensing region a different value of anelectrical parameter is measurable between said sensing region and afirst reference voltage so as to determine a drift direction of theprobe.

The sensing structure may be advantageously arranged so that the atleast one sensing element is further connected to at least one adjacentfirst sensing element. Advantageously, the first sensing elements may beconnected in series.

In this manner, the sensing regions included in the structure areconnected to a reference potential through one of more sensing elements,wherein the sensing elements are shared among the sensing regions. Thisallows for cumulating the effect of the sensing elements so as to createbetween the sensing regions a voltage or potential difference thatallows unambiguous determination of the position of a probe, while usinga reduced number of sensing elements arranged in a compact design.

Advantageously, the sensing regions may be arranged such that thedifference in the value of the measured electrical parameter of twoadjacent sensing regions is increased for each pair of adjacent sensingregions. In this manner an average difference in the value of theelectrical parameter of two adjacent sensing regions may be increased.Accordingly, using a limited number of sensing elements it is possibleto generate large potential differences between adjacent sensing regionsso as to reliably determine the position of a probe.

The sensing structure may advantageously be connected to a secondreference potential. Accordingly, one of the first and second referencepotentials may be selectively connected to the power supply voltage,while the remaining reference potential may be connected to a groundpotential. The sensing structure according to this configuration maytherefore be used actively during normal operation of the integratedcircuit.

According to an embodiment, the sensing regions may at least partiallysurround a probe region chosen so as to correspond to a conductiveregion adapted to be connected to an integrated circuit. Since the proberegion may also be the conducting region or pad of an integratedcircuit, if a probe is detected as lying outside the probe region it ispossible to conclude that the probes used for testing the integratedcircuits in the wafer are not correctly centered, thereby allowing forcorrecting the position of the probe.

Advantageously, the probe region may coincide with one of the sensingregions. In this manner if the probe is within the probe region it ispossible to measure a potential, thereby allowing to reliablydistinguish whether the probe is within the probe region or in anon-conductive region surrounding the sensing structure.

Alternatively, the probe region may be an electrically conductivematerial connected to a ground electrode by means of a protectionelement. In this embodiment, the sensing structure can be used, incontrast to a dummy structure, as an active structure for connecting theintegrated circuit to other systems external to the integrated circuit.

Advantageously, the sensing elements may be adapted to conduct a currentin a unidirectional manner. In particular, any of the first and secondsensing elements and the protection element may include at least a setor a subset of elements chosen among diodes and transistors, suitablyconnected. Alternatively, resistors, inductors, capacitors, ortransmission lines may be used instead as elements adapted to conduct acurrent in a unidirectional manner.

In an advantageous embodiment, the first sensing element and theprotection element have opposing polarizations.

According to a second aspect, an embodiment provides a sensingarrangement including a plurality of sensing structures, wherein atleast one sensing region of a first sensing structure is connected to asensing region of a second sensing structure. Accordingly, it ispossible to form clusters of sensing regions connectable to an array ofprobes all connected to the same sensing elements. This configurationallows reducing the space of a substrate exclusively dedicated to thesensing structure.

The sensing arrangement may also include a plurality of sensingstructures wherein the sensing structures are arranged in one or morerows, each row having at least one common sensing region. Moreover,sensing regions of different row may be connected by means of a sensingelement.

According to a further aspect, an embodiment relates to a substrate forintegrated circuits comprising one or more sensing structures. By meansof said sensing structures it is possible to determine whether a matrix,or set or array of probes including a plurality of probes for testingintegrated circuits is aligned with respect to the substrate such thateach probe is connectable with the corresponding terminal or pad of theintegrated circuit.

Advantageously, the substrate may include a passivation surrounding theprobe region of each sensing structure and the sensing regions may beformed over the passivation.

The plurality of sensing structures may be arranged on the substrate soas to be connected with respective probes located at the extremities ofa probing head. Since the behavior of probes along the edges of a matrixof probes are more largely affected by misalignment, the above describedarrangement allows determining with higher precision a misalignment ofthe probes in the probe card with the corresponding pads.

Moreover, in a further arrangement the sensing structures may bearranged on the substrate based on the moving direction of the probe.Aligning the sensing structure according to the moving direction of aprobe allows for reducing the number of sensing regions needed tounambiguously determine the position of the probe.

Embodiments also relate to testing equipment for testing electroniccomponents in a substrate. The testing equipment includes a probe headcomprising one or more probes connectable to respective sensingstructures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated into the specification andform part thereof to illustrate several embodiments. These drawingstogether with the description serve to explain the principle of theinvention. The drawings are only for the purpose of illustratingpreferred and alternative examples of how the invention can be made andused, and are not to be construed as limiting the invention to only theillustrated and described embodiments. Further features and advantageswill become apparent from the following and more particular descriptionof the various embodiments of the invention, as illustrated in theaccompanying drawings, in which like reference numbers refer to likeelements, wherein:

FIG. 1 is a schematic drawing illustrating a sensing structure for usein testing integrated circuits on a substrate;

FIGS. 2 to 5 are schematic drawings illustrating alternativerealizations of the sensing structure of FIG. 1;

FIG. 6 is a schematic drawing illustrating a sensing structure;

FIGS. 7 to 10 are schematic drawings illustrating a sensing arrangement;

FIG. 11 is a schematic drawing illustrating a sensing arrangement;

FIGS. 12 and 13 are schematic drawings illustrating the sensingarrangement of FIG. 11 during operation;

FIG. 14 is a schematic drawing illustrating a sensing arrangement;

FIG. 15 is a schematic drawing illustrating the sensing arrangement ofFIG. 14 during operation;

FIGS. 16 to 18 are sectional views of a sensing structure according toalternative realizations;

FIG. 19 shows a sectional view of a substrate comprising a sensingstructure according to the realization of FIG. 18;

FIGS. 20 to 24 are schematic drawings illustrating further examples ofthe sensing structure;

FIGS. 25 to 28 are schematic drawings illustrating possible arrangementsof a plurality of sensing structures;

FIGS. 29 to 31 are schematic drawings illustrating substrates forintegrated circuits;

FIG. 32 is a schematic drawing illustrating a testing system;

FIG. 33 is a detailed block diagram illustrating design steps forrealizing a substrate for integrated circuits and a probe card fortesting the substrate;

FIGS. 34 and 35 are schematic drawings illustrating sensing structuresaccording to the prior art;

FIG. 36 is a histogram showing the results of several measurements of asensing structure in optimal conditions; and

FIG. 37 is a histogram showing the results of measurements performed ona sensing pad in non-optimal conditions.

DETAILED DESCRIPTION

In the following description, for explanatory purposes, specific detailsare set forth in order to provide a thorough understanding of the ideasof the present invention. However, it may be evident that the presentinvention can be practiced without using these specific details.Furthermore, well know structures and devices are only described ingeneral form in order to facilitate the description thereof.

One problem is based on the observation that with the progress inphoto-lithographic technologies, substrates for integrated circuits,such as wafers including integrated circuits, include an increasinglylarge number of connecting pads closely arranged next to each other.Correctly aligning a probe with the corresponding connection terminal onthe substrate during the testing phase has therefore become crucial inorder not to damage the area surrounding the connection terminal itself.Said connection terminal may be, for instance, a pad or a bump(protruding contact bump).

Correct alignment of a probe and its corresponding pad can be performedmanually by directly checking a mark of the probe (probe mark) left bythe tip of the probe on the pad after having performed the testingprocedure. However, the increasing need for integrated circuits capableof working at high temperatures requires using very robust materials forthe pads and electric connections. Consequently, the probe mark is notalways visible on hard materials, thereby making it impossible tovisually verify the correct alignment of the probe with thecorresponding pad. Therefore, it has become necessary to electronicallyverify alignment by connecting the tip to specially designed structuresand analyzing the value of an electrical parameter for example afterforcing an excitation such as a current onto the structure. Saidexcitation may preferably be continuous but it could alternatively bealso variable. However, this kind of measurement sensibly variesdepending on the quality of the connection between the probe and thecorresponding pad. For example, between the tip of a probe and thecorresponding pad often lie oxides and contaminants, which reduce theelectrical contact surface between the probe and the pad itself, therebydeteriorating the electrical performance of the contact. This canincrease the resistance between the probe and the corresponding sensingstructure and thus produce sensible variations in the measuredelectrical parameters. As a result the testing procedure may produceincorrect results.

According to at least one embodiment, in order to check the position ofthe probe, a sensing structure is designed to be insensitive to problemsdue to poor or non-optimal electrical contacts between the sensingstructure and the probe.

FIG. 1 illustrates a sensing structure 100 including a plurality ofconducting sensing regions 110 or sensing regions. Generally, thesensing regions 110 may be a pad or a bump on the surface of thesubstrate or wafer. However, any other conducting structure electricallyconnectable to a conducting element may be used as sensing region 110.The sensing regions 110 are surrounded by an insulating material so asto be electrically isolated. The sensing structure 100 further includesa second region 120, whose dimensions and shape may resemble those of aconnection terminal for connecting to a circuit integrated in thesubstrate. The second region 120 corresponds to a probe region.

In one embodiment, the probe region 120 is non-conductive. However, theprobe region 120 can be made of a conducting material. Further, althoughin this embodiment, the probe region 120 has dimensions substantiallyequivalent to those of a connecting terminal of an integrated circuit tobe tested, in other advantageous embodiments, the probe region 120 maybe chosen as being smaller than the area of a generic pad of anintegrated circuit, so as to increase the sensibility and reliability ofthe sensing structure 100.

The sensing regions 110 are connected to a detecting circuit 135 orsensing circuit, which may advantageously comprise a plurality ofsensing elements 130 connected to each other in series. Each of thesensing elements 130 is directly connected to two sensing regions 110,such that each pair of sensing regions 110 is connected to at least onesensing element. The sensing structure 100 is connectable to a referenceelectrode at a predetermined potential V_(sr) so that if a probe inducesa current flow onto one of the sensing regions a voltage drop can bemeasured between the sensing region and the reference potential. Saidreference potential will be obtained, for instance, through a connectionelectrode or terminal (not shown in FIG. 1), which is in turn connectedto a probe at the reference potential. A current can be induced in thesensing region by creating, across the sensing region 110 and thereference electrode, an appropriate potential difference.

The sensing element 130 is adapted to have a defined voltage drop acrossits terminals and can include a suitable electronic circuit comprisingone or more electrical components. As depicted in FIGS. 2 and 3, thesensing elements may be diodes 131. The sensing diodes 131 may be, forinstance, parasitic diodes in the integrated electronic structureincluded in the substrate and to which said sensing region is connected.In this manner, the dimensions and costs of the sensing structure can bedrastically reduced. However, the sensing element 130 may also be atransistor 132, which in FIG. 3 is suitably connected so as to form atransdiode, or a resistor.

Although FIGS. 1 to 3 illustrate an example of sensing structure 100including three sensing regions 110, the sensing structure 100 mayinclude any number of sensing regions 110. The number of sensing regions110 may be chosen according to the level of accuracy needed forverifying alignment. Further, although the probe region 120 in FIGS. 1to 3 is square-shaped, it may be designed to have any shape. As anexample, the probe region 120 may be rectangular, hexagonal, octagonal,polygonal, circular, or elliptical. Similarly, also the sensing regions110 may be designed to have any shape, like for example, one of theshapes listed above. This holds also true for the probing and sensingregions of the other following embodiments.

FIG. 4 schematically illustrates the use of a sensing structure 100including eight sensing regions 110 connected to a series of sensingdiodes 131. If a probe 140 is within the insulating probe region 120,there will be no current flowing to the sensing diodes 131, since theprobe 140 contacts an insulating material. In this case, the probe canbe considered to be correctly aligned.

On the other hand, if the probe 140 contacts one of the sensing regions110, a current can flow from the probe 140 to the electrode of thereference potential, thereby indicating that the probe 140 is misalignedwith respect to the probe region 120. The drift direction of the probe140 can be determined by measuring the voltage drop across the sensingdiodes. In this particular example, the reference potential is a groundpotential and the voltage drop between a sensing region and the groundpotential is the sum of the voltage drops across the sensing diodes 131between the sensing region 110 and the ground potential. Since thesensing diodes 131 are connected in series, the voltage measured onadjacent sensing regions will be at least equal or greater (due to thewell known non linear characteristic of the diode) to the thresholdvoltage V_(th) of the particular sensing diode used in the circuit. Inthe example of FIG. 4, the sensing regions 110 are suitably connected tothe sensing diodes 131, so as to create a voltage difference betweenadjacent sensing regions of at least 3·V_(th).

The probe 140 may be part of a matrix of probes included in a testingsystem, and said matrix of probes may simultaneously contact a pluralityof conducting regions on a substrate. Further, the testing system may becalibrated so as not to be affected by measuring errors due todeteriorated electric contacts or in non-optimal conditions. Forexample, as shown in FIG. 4, the testing system may be calibrated so asto verify, by means of a suitable electrical test, whether the voltagemeasured by the probe 140 lies within a predetermined voltage intervaldefined by a parameter k appropriately chosen based on the particularcircuit to be electrically tested and on the used testing system towhich the probes belong.

Advantageously, the probe region 120 has a circular shape and as aconsequence, the check of the position of the probe 140, performedthrough the sensing structure 100, does not depend from the movingdirection of the probe 140 itself.

Advantageously, knowing the moving direction of the probe 140, it ispossible to suitably induce the potentials on the various sensingregions 110 based on the particular needs.

The sensing diodes 131 included in the sensing circuit 135 may also havean opposite polarization with respect to the sensing diodes 131 depictedin FIG. 4. In this case, the current will flow in the oppositedirection. This example is shown in FIG. 5. The current induced onto thesensing structure 110 may be thus provided by a special probe connectedto a reference terminal in the substrate, which is here connected toground. Alternatively, the current may be provided/absorbed through asupport on which the wafer is arranged.

FIG. 6 illustrates a sensing structure 200, including a probe region 115made of a conducting material and connected to a sensing diode 131 ofthe sensing circuit 135. If the probe region 115 is connected to thesensing circuit 135, it may be considered to be an additional sensingregion. During the test procedure, if the probe 140 is within the proberegion 115, an electrical connection will be established between theprobe 140 and the probe region 115. Consequently, a current will flowthrough the sensing circuit 135 and the probe 140 will measure apotential given by the sum of the threshold potentials of sensing diodes131 connected to the probe region 115 in series. In FIG. 6, eightsensing diodes having the same characteristics are connected in seriesto the probe region 115 and the ground electrode. Considering thepolarization of the diodes 131, the probe will measure a voltage of atleast −8·V_(th) if the probe 140 contacts the sensing structure 200within the probe region 115.

As shown in FIGS. 7 and 8, since probe region 120 of the sensingstructure 100 illustrated in FIGS. 1 to 4 is non-conductive, saidsensing structure is not capable of determining whether the probe 140 isaligned on the probe region or on any other non-conductive regionoutside the sensing structure 100. On the contrary, in the sensingstructure 200 of FIG. 6, a predefined voltage value can be measured ifthe probe 140 contacts the sensing structure 200 within the probe region115. Accordingly, the sensing structure 200 allows determining whetherthe probe 140 contacts the probe region 115 or any other non-conductivearea outside the sensing structure 200.

FIGS. 9 and 10 illustrate a situation, wherein more than one sensingregion 110 and 115 are simultaneously contacted by the probe 140. Sincethe sensing regions 110 and 115 are connected to the same circuit ofsensing diodes 131 connected in parallel, the current will flow onlythrough the circuit portion that offers less resistance or, in otherwords, through the path including the smaller number of sensing diodes131. More precisely, since the sensing regions are short-circuited, thepotential drop of the series of diodes between these regions will bezero and these sensing diodes will be non-conducting. Therefore, thecurrent will flow through the remaining diodes connecting theshort-circuited sensing regions 110 to the reference potential, and theprobe 140 will measure a voltage value given by the sum of the thresholdvoltages of the diodes crossed by the current. Hence, although two ormore sensing regions are short circuited, the probe 140 will assume thepotential closest to the ground potential.

More precisely, in FIG. 9 the probe 140 short circuits the sensingregion 110 directly connected to a ground electrode and the sensingregions 110 and 115 connected to the ground electrode through 7 and 8sensing diodes 131, respectively. In this example, all the sensingdiodes 131 of the sensing circuit 135 will be at the same potential andthe current will flow through the connection line directly connected tothe ground electrode. As a consequence, the probe 140 will measure anull voltage.

Similarly, in the example of FIG. 10, the probe 140 short circuits thesensing region 115 connected to the ground through eight sensing diodes131 and the sensing region 110 connected to the ground through foursensing diodes 131. Again, the sensing diodes 131 connected to thesensing regions 110 and 115 are at the same potential. Therefore,current will flow only through the first four sensing diodes 131connecting the sensing regions 110 to the ground electrode and the probe140 will measure a voltage of −4·V_(th).

The probe region 115 may also be connected to a protection element 133for protecting circuits from electrostatic discharge and belonging tothe ESD (ElectroStatic Discharge) protection circuits. Such protectionelement may be a diode.

FIG. 11 shows a sensing structure 300 where the probe region 115 isconnected to the ground electrode through a protection diode 133, whilethe sensing regions 110 are connected to the sensing circuit 130. Theprotection diode 133 and the sensing diodes 131 have opposingpolarizations. If the probe 140 contacts the probe region 115, a currentwill flow through the protection diode 133 and the probe region 115 willassume a potential of −V_(th). On the contrary, if the probe 140contacts one of the sensing regions 110, a current will flow through thesensing diodes 131 and the probe 140 will measure a positive voltagevalue given by the sum of the voltage drops across the sensing diodes131 conducting the current. In other words, if the probe 140 contacts asensing region 110, the same will be crossed by a current flowing in theopposite direction with respect to the current flowing through theprotection diode 133. Therefore, if during the testing procedure it ispossible to induce a current in both directions, it can be assumed thatthe probe 140 is short circuiting at least one sensing region 110 andthe probe region 115.

Since the probe region 115 is connected to the ESD protection diode 133,the sensing structure 300, or more precisely the probe region 115, canalso be advantageously used for connecting an integrated circuit in thesubstrate to the other external electrical systems and can therefore beused, for instance as a generic traditional pad during normal operationof the integrated circuit. At the same time, the probe region 115 mayalso be used as a detecting region in a similar manner as the sensingregion 110.

Although the diodes 131 were used as sensing elements 130, the sensingelements 130 may be formed by other electronic components, such as, forinstance, transistors or resistors and each sensing element 130 mayinclude one more of these components.

FIGS. 12 and 13 illustrate two examples of an operation of the sensingstructure 300. More precisely, in the example of FIG. 12, the probe 140contacts both the probe region 115 and the sensing region 110, which isconnected to the ground electrode through 5 sensing diodes 131. In thiscase, the current can flow through the probe in two directions and theprobe 140 will measure a potential of at least −V_(th) if the currentflows through the protection diode 133 or it will measure a value of atleast 5·V_(th) if the current flows through the sensing circuit 130. Asshown in FIG. 13, if the probe short circuits more than one sensingregion 110 and the probe region 115, if current flows through thesensing circuit 130, the probe will assume the potential closer to theground potential.

On the contrary, if the current can only flow in one direction, theprobe 140 will be contacting only with the probe region 115 or only withthe sensing regions 110.

In FIG. 11 the sensing circuit 130 and the protection diode 133 are bothconnected to a ground electrode. However, it is also possible to providea sensing structure 300 wherein the sensing circuit 130 is connected toa reference potential V_(sr) different from the ground potential, asshown in the example in FIGS. 14 and 15. In this example, if the probe140 contacts a sensing region 110, it will measure a potential valuereferred to the reference voltage V_(sr).

FIGS. 16 to 18 show a sectional view of a sensing structure 100, 200 and300. In FIG. 16, the probe region 115 and the sensing regions 110 areintegrated in a first non-conductive layer 400. Moreover, a passivationlayer 410 lies on top of the first non-conductive layer 400 andsurrounds the sensing regions 110 and the probe region 115. The sensingstructure 100, 200, 300 may protrude from the passivation.Alternatively, as shown in FIG. 17, the sensing structure 100, 200, 300is integrated in the first non-conductive layer 400 and is surrounded bya passivation layer 410. The sensing structure 300 may be arranged inthe first non-conductive layer 400 such that the sensing regions 110 andthe probe region 115 do not protrude from the first non-conductivelayer. In this example, the passivation layer 410 surrounds the sensingstructure 100, 200, 300 but does not lie between the sensing regions 110and the probe region 115. The sensing regions 110 and a probe region 115are isolated by means of the first non-conductive layer 400.

FIG. 18 shows an alternative realization of the sensing structure 100,200, 300. Accordingly, the probe region 115 is in the firstnon-conductive layer 400, is surrounded by a passivation layer 410 andprotrudes from the latter. In this example, the sensing regions 110include conductive material, such as a metal arranged on the passivationlayer 410. Since the sensing regions are only used in the testing phasefor verifying alignment of the probe 140, they are not exposed toexcessive mechanical stresses. Therefore, the sensing regions 110 arecreated using only one level of conductive material, such as a metal,and are connected to the sensing circuit 135 by means of a small pad 112in the passivation layer 410 and by means of vias connections 420(vertical interconnect accesses) and metal lines or metals 430. On theother hand, since the probe region 115 is exposed to high mechanicalstresses during the testing phase and during assembly of the packageddevice, it will be realized using several metallization levels ormetals.

FIG. 19 shows a detailed sectional view of the connection between thesensing region 110 and the metals in the non-conductive substrate 400.Since in the examples of FIGS. 18 and 19 only the probe region 115 isrealized using several layers of metal, it is possible to reduce thespace/volume needed for realizing the sensing structure 100, 200, 300.

In the aforementioned sensing structures the sensing regions 110 and theprobe region 115 may be pads which are finished in NiPd or NiPdAu.

The structure and the design of the sensing structure 100, 200, 300 canbe optimized and simplified knowing the movement, slide or scrubdirection of the probe 140 on the probe region 115 or on the pad. Inparticular, if the probe 140 moves on the substrate only in onedirection, the sensing regions can be reduced to two. Alternatively, ifthe probe region 115 includes connection terminals or conductive padsconnected to the integrated circuit, the sensing structure may bedesigned so as to include one sensing region 110 and one probe region115.

FIGS. 20 to 22 illustrate several examples of a sensing structure 200,300 optimized based on the scrub direction 145 of the probe 140. Moreprecisely, FIG. 20 shows a sensing structure 200, 300 including a proberegion 115 and two sensing regions 110. Advantageously, the probe region115 is here rotated by 45 degrees with respect to common probe regionsor pads that have generally a square or rectangular shape and aligned.Thus, the probe 140 will have a larger area on which it can slide,thereby allowing reducing the area of the probe region 115. The sensingregions 110 and the probe region 115 are connected to the correspondingsensing elements 130 as described above. Moreover, the probe region 115is further connected to a reference potential through a further sensingelement 130. If the reference potential is the ground voltage and thesensing elements 130 are sensing diodes 131, the probe region 115 can beused as an active region, as for instance a pad for connecting anintegrated circuit with other systems. FIGS. 21 and 22 illustratealternative design of a sensing structure 200, 300 including a proberegion 115 and a sensing region 110. The sensing structure isadvantageously simplified by including only one sensing region 110,thereby reducing the complexity of the structure and the space occupiedby the complete sensing structure 100, 200. FIGS. 21 and 22alternatively illustrate sensing structures 200, 300 including twosensing regions 110.

The sensing regions illustrated in FIGS. 20 to 22 can also be connectedto two connection terminals or pads or electrodes.

FIGS. 23 and 24 illustrate an example of such a sensing structure.Although the example describes a sensing structure 200, 300 includingtwo sensing regions, or a sensing region 110 and a probe region 115, itmay be possible to design sensing structures including any number ofsensing regions. According to FIG. 23, the probe region 115 is connectedto a ground electrode through a diode 131. This diode can be seen as aprotecting element 133 and in this case the probe region 115 results inbeing connected to an ESD protection element. Further, the sensingregion 110 is connected to a reference potential V_(sr). If thereference potential is chosen as being a power supply voltage, thesensing structure may be also used as an active structure included inthe ESD protection circuits.

During operation of the sensing structure 200, 300 the referencepotential V_(sr) and the ground potential may be provided by means of aground probe 141 and a reference voltage probe 142 connected torespective ground and reference pads.

In order to determine the position of the probe 140 a current may beinduced from the ground pad to the probe 140. If between the groundprobe 141 and the probe 140 and between the probe 140 and the referenceprobe 142, the same voltage V_(th), is measured, the probe 140 will bewithin the probe region 115. Otherwise, if between the ground probe 141and the probe 140 is measured a voltage of at least 2·V_(th), whilebetween the probe 140 and the reference probe 142 is measured a nullvoltage, the probe 140 will be on the sensing region 110. Finally, ifbetween the ground probe 141 and the probe 140 is measured a voltage ofV_(th), while between the probe 140 and the reference probe 142 ismeasured a zero voltage, it can be derived that the probe 140 is incontact with both the probe region 115 and the sensing region 110. Inthis case, between the ground probe 141 and the reference probe 142 ismeasured a tension of V_(th).

Although the sensing structure 200, 300 of FIGS. 23 and 24 is connectedto the power supply voltage by means of a pad and to ground by means ofanother pad, during the testing phase the sensing structure 200, 300 maybe connected to any reference potential different from the power supplyand/or ground potential.

According to an embodiment, a sensing arrangement 450 including aplurality of sensing structures 100, 200, 300 is provided.

As illustrated in FIG. 25, the sensing arrangement 450 includes twosensing structures 100, 200, 300 connected to each other by means of asensing element 130. In the particular example of FIG. 25, the sensingregions 110 of two sensing structures 100, 200, 300 are connectedthrough a sensing diode 131.

FIG. 26 shows a sensing arrangement 450 including a cluster of sensingstructures 100, 200, 300. Said cluster may include several activeregions and a sensing region 110 common to several sensing structures100, 200, 300. Adjacent clusters may be further connected through asensing diode 131.

The sensing arrangement 450 may also include one or more rows of sensingstructures 100, 200, 300, as illustrated in FIG. 27. According to thisembodiment sensing structures 100, 200, 300 in the same row may have acommon sensing region 110 which may be arranged based on the movingdirection of an array of probes 140. Further, the sensing structures100, 200, 300 may be connected to a reference potential and to a groundpotential as described in the example of FIGS. 23 and 24. According tothis arrangement, since all the sensing regions 110 are connected toeach other, only one of the sensing regions 110, has to be connected tothe ground terminal in order to have an array of active sensingstructures 100, 200, 300.

Although in the example of FIG. 27 only one sensing region is providedfor each array of sensing structures 100, 200, 300, it is also possibleto have arrays of sensing structures 100, 200, 300 including two or moresensing regions as shown in FIG. 28. This realization is particularlyuseful if the moving direction of the array of probes 140 is not known.

A substrate 500 for integrated circuits may include the sensing regions100, 200, 300 or the sensing arrangement 450. The substrate 500 may be,for instance, a wafer. As illustrated in FIG. 29 the sensing structures100, 200, 300 may be located in the area 510 of the integrated circuitor may be located in a separation line or scribe line 520 locatedbetween adjacent device areas 510 on the substrate 500. Alternatively,the sensing structures 100, 200, 300 and the sensing arrangement 450 maybe arranged on a dummy substrate that does not include any integratedcircuits to be tested.

Advantageously, if the sensing structure 100, 200, 300 and the sensingarrangement 450 are located in the scribe line 520, said structures willnot occupy space in the integrated circuit area 510 which may beentirely dedicated to said integrated circuit. Moreover, if the sensingstructures in the scribe line include an active sensing structure 100,200, 300, due to a connection terminal or pad, this can be used fortesting elementary circuits or TEG (Test Element Group) located in thescribe line of the substrate.

As shown in FIGS. 30 and 31, the sensing structures 100, 200, 300 andthe sensing arrangement 450 may be located along the edges of theintegrated circuit 510. Alternatively, the sensing structures may belocated in correspondence of critical probes 140 of the array, such asperipheral probes or longer probes 140 of the array of probes of theprobe card. Since the sensing structures 300 can also be used forconnecting to integrated circuits, the integrated circuit 510 may bedesigned for including only sensing structure, which will be used forverifying alignment of the probes 140, for testing the integratedcircuits of the substrate, and as connection terminals in the endproduct.

Equipment for testing integrated circuits in the substrate 500 ispartially shown in FIG. 32, and includes a probe array 150 including atleast one probe 140. The probe array 150 may connect to probe card 160including a printed circuit board, and the substrate 500 including atleast one sensing structure 100, 200, 300. The substrate 500 may bearranged onto a support 600 chuck and included into a device proberwhich is not shown here.

The optimal design of the position of the sensing structures 100, 200,300 on the integrated circuit 510 essentially depends on the design ofthe circuit elements forming said integrated circuit 510 and on thescrub direction of the various probes 140. Therefore, in order to reducethe number of sensing regions needed for verifying the position of theprobes 140, it may be advantageous to jointly design the integratedcircuit 510 and the probe card 160. This process is schematicallyillustrated in the flow diagram of FIG. 33. More precisely, the probecard 160 to be used in the testing phase will be designed based on thedesign of the integrated circuits 510 on the substrate 500.Subsequently, the probe card 160 so produced may be used for performingthe electrical test on the EWS on the substrate 500 and finally, theintegrated circuit device can be assembled.

If the sensing structures 100, 200, 300 are placed in the scribe line520, the joint design of the probe card and lithographic masks has to beperformed by placing the sensing structures 100, 200, 300 in the arrayof integrated circuits that said mask will realize.

Therefore, the embodiments relate to improved sensing structures 100,200, 300 capable of unambiguously determining a drift direction of aprobe 140 with respect to the sensing structure 100, 200, 300 withoutbeing affected by variations in the measured values due to non-optimalelectrical contacts between the sensing structure 100, 200, 300 and aprobe 140.

In the embodiments, the electrical connection between the sensingstructure 100, 200, 300 and the probe 140 is obtained by contacting theprobe 140 with the sensing regions 110 and 115. However, in a furthernot illustrated embodiment, the probe 140 may be electrically connectedto the sensing structure 100, 200, 300 by other means that do notnecessarily require a direct electrical contact between probe 140 andsensing structure 100, 200, 300. As an example, in the case that thesensing structure and the probe can operate at radiofrequencies, the tipof the probe 140 may be for instance used as a capacitive interfaceconducting a variable current. Consequently, the sensing elements 130may also include responsive elements such as inductances or capacitorsor transmission lines. In any case, such a structure may be useful ifthe probe 140 operates at radiofrequencies.

Of course, in order to satisfy contingent and specific requirements, askilled person may apply several modifications to the previouslydescribed solutions. Although the present invention has been describedwith reference to preferred embodiments, it should be clear that variousomissions, replacements and modifications in the design and details,such as other embodiments are possible; it is further clearly intendedthat specific elements and/or method steps described in relation withany embodiment of the described invention ca be incorporated in anyother embodiment in conjunction with the state of the art as generalaspects of design choices.

The invention claimed is:
 1. A sensing structure for use in testing anintegrated circuit on a substrate, the sensing structure comprising: aconductive probe region; a first sensing region at least partiallysurrounding the conductive probe region; and a plurality of sensingelements connected in series; wherein a first sensing element of theplurality of sensing elements has two terminals respectively connectedto the first sensing region and the conductive probe region; wherein asecond sensing element of the plurality of sensing elements has twoterminals respectively connected to the conductive probe region and afirst reference potential.
 2. The sensing structure of claim 1, whereineach sensing element comprises a diode or a transistor.
 3. The sensingstructure of claim 1, further comprising additional sensing regions andfor each additional sensing region a different value of an electricalparameter is measurable between the additional sensing region and thefirst reference potential for determining a drift direction of theprobe.
 4. The sensing structure of claim 1, wherein the first sensingregion is further connected to a second reference potential and one ofthe first and second reference potentials is a ground potential.
 5. Thesensing structure of claim 4, further comprising an additional proberegion; a further probe region; a second sensing region at leastpartially surrounding the additional probe region, and wherein the firstsensing region at least partially surrounds the additional and furtherprobe region.
 6. The sensing structure of claim 1, wherein theconductive probe region has a diamond shape in a top view and the firstsensing region partially surrounds two sides of the diamond shape of theconductive probe region.
 7. The sensing structure of claim 1, furthercomprising a reference pad and a ground pad respectively connected tothe first and the second sensing elements, wherein the reference pad isconnected to a reference voltage probe for providing a second referencepotential and the ground pad is connected to a ground potential forproviding the first reference potential.
 8. A sensing structure for usein testing an integrated circuit on a substrate, the sensing structurecomprising: a conductive probe region; a first sensing region at leastpartially surrounding the conductive probe region; and a plurality ofsensing elements connected in series; wherein a first sensing element ofthe plurality of sensing elements has two terminals respectivelyconnecting the first sensing region to a first reference potential and afirst terminal of a second sensing element of the plurality of sensingelements; and wherein the second sensing element has a second terminalconnected to the conductive probe region.
 9. The sensing structure ofclaim 7, further comprising a second conductive probe region and asecond sensing region at least partially surrounding the secondconductive probe region, and a third sensing element connecting thefirst sensing region to the second sensing region.
 10. The sensingstructure of claim 7, further comprising a fourth sensing elementconnecting the second conductive probe region to the first referencepotential.
 11. The sensing structure of claim 9, further comprising athird conductive probe region adjacent to the first sensing region andthe second sensing region electrically connected to the first sensingregion as a continuous conductive sensing region; and a fourth sensingelement connecting a third sensing region partially surrounding thethird conductive probe region to the first and the second sensingregions.
 12. The sensing structure of claim 11, wherein the first, thesecond, and the third sensing regions partially surround all the first,the second, and the third conductive probe regions.
 13. A substrate forintegrated circuits, comprising: a conductive probe region; a pluralityof sensing regions partially surround the conductive probe region andconnectable to a probe; and a plurality of sensing elements connecting,in series, the plurality of sensing regions to the conductive proberegion; wherein each of the plurality of sensing elements has twoterminals connecting two of the plurality of sensing regions, and aprobe sensing element connecting the plurality of sensing elements tothe conductive probe region.
 14. The substrate of claim 13, wherein theconnection between the probe sensing element and the plurality ofsensing elements is further connected to a ground reference potential.15. The sensing structure of claim 13, wherein the conductive proberegion has a round shape and the plurality of sensing regions each hasan arc shape partially surrounding the conductive probe region.
 16. Thesensing structure of claim 13, wherein the probe sensing element and theplurality of sensing elements include a diode or a transistor.
 17. Asubstrate for integrated circuits, comprising: a conductive proberegion; a probe sensing element connecting a ground terminal to theconductive probe region; a plurality of sensing regions partiallysurround the conductive probe region and connectable to a probe; and aplurality of sensing elements connecting, in series, the plurality ofsensing regions to each other, wherein each of the plurality of sensingelements has two terminals, each of the two terminals connecting to oneof the plurality of sensing regions.
 18. The substrate of claim 17,wherein one of the plurality of sensing element is provided with areference voltage potential.
 19. The sensing structure of claim 17,wherein the conductive probe region has a round shape and the pluralityof sensing regions each has an arc shape partially surrounding theconductive probe region.
 20. The sensing structure of claim 17, whereinthe probe sensing element and the plurality of sensing elements includea diode or a transistor.